It is imperative that communications cables be grounded to discharge damaging and/or annoying induced energy resulting from transient surges (caused by lightning, transient voltages and power crosses), periodic signals (such as sixty cycle interference from power lines) and other known causes. Conventional cable sheath grounding methods require a fixed electrical connection at selected locations (typically at cable splice points) between the cable sheath and earth ground. Grounding of the cable sheath at each splice point provides a plurality of signal paths for bleeding off induced energy present on the sheath and protecting the cable and associated communications equipment from damage and interference.
With buried communications cables, however, facilitating long range cable locating using conventional signal radiating techniques is equally imperative to protecting the cable from induced energy. In the conventional locating method, a locating signal is transmitted along the length of the cable sheath. The cable sheath functions as an antenna radiating the transmitted locating signal through the earth for subsequent surface detection. The strength of the received radiated signal gives an indication of the approximate location of the buried communications cable.
Fixed grounding of the communications cable sheath as described above, however, precludes long range cable locating using conventional signal radiating techniques because the locating signal transmitted on the cable sheath will be shunted to ground at the first cable splice point encountered along the length of the cable. Thus, to enable long range cable locating, the ground connection at each splice point must be disconnected (lifted) by cable maintenance personnel to allow the locating signal to propagate along the entire length of the communications cable. Over the course of a thirty to sixty mile length of communications cable, it becomes prohibitively inconvenient, inefficient and expensive to have the ground connection lifted at each one of dozens of splice points.
Of further concern with respect to long range cable locating is the difficulty experienced with locating communications cables on side legs (or spurs) emanating from a main communications cable. Due to the potential differences in impedance of the sheath caused by differences in side leg lengths, it is likely that the cable locating signal will propagate at different, sometimes insufficient strengths, down each side leg. If the locating signal has insufficient signal strength, radiation from the sheath and surface detection may become difficult or impossible, thus adversely affecting the accuracy of the cable locating activity.